1. Field of the Invention
The present invention relates to a protective film for a flat panel display (FPD) such as a plasma display panel (PDP), a plasma addressed liquid crystal display (PALC), and the like and an FPD in which the protective film is used, a vapor deposition material suitable for forming a protective film for FPD and its production method, and a device for manufacturing an FPD protective film.
2. Description of Related Art
During the past several years, there has been considerable activity in the research and development as well as practical application of liquid crystal displays (LCD) and various other types of flat displays, and production of these displays is also increasing rapidly. There has recently also been growing activity in the development and practical application of color plasma display panels (PDP). PDP are easily applied to large screens, and are the easiest way to achieve large-screen wall-mounted televisions for Hi-Vision applications, and prototypes of PDP offering a diagonal size of 40 inches have already been developed. In the case of FPD, which include these PDP, the glass dielectric layer is directly exposed to electrical discharge, and the surface of the dielectric layer changes due to sputtering of ion collisions resulting in a rise in the discharge starting voltage. Consequently, various oxides having a high heat of sublimation have been used as protective films.
In the past, known examples of depositing this protective film included methods involving the formation of an FPD protective film using a vacuum process such as electron beam vapor deposition, sputtering and ion plating. In the case of electron beam vapor deposition and ion plating, the vapor deposition material serving as the raw material for forming the protective film, and the FPD on which the protective film is formed, are placed in a vacuum container, the vapor deposition material is heated under a high vacuum, or evaporated using an electron beam or plasma, and vapor is agglutinated in the form of a thin film on the surface of the FPD.
On the other hand, since a PDP protective film is in direct contact with the discharge space, it serves as the key material for fulfilling the most important role for discharge characteristics, and an MgO film was used in the past due to its high secondary electron discharge capabilities and superior sputtering resistance, light transmission and insulating properties.
However, if this MgO film is exposed to the atmosphere during the course of processing, it deteriorates easily as a result of reacting with CO2 and H2O. Therefore, it is known that degassing exhaust treatment over a long period of time while heating in a vacuum after sealing the film on the panel is required in order to obtain the inherent characteristics of MgO (see, for example, Sato, ed., Current Plasma Display Production Technology (Press Journal Co., Ltd.): p. 118-123 and p. 291-295 (1997)). According to this, impurity gases such as H2O, H2, O2, CO, CO2 and N2 have a detrimental effect on PDP discharge characteristics and composite materials in the panel, and contamination by CO2 in particular can worsen panel characteristics beyond recovery.
Consequently, the coating of the MgO surface with another material having low moisture permeability has been proposed in order to prevent deterioration of MgO (Japanese Unexamined Patent Application, First Publication No. 10-149767, W. T. Lee et al.: “LaF3 coated MgO protecting layer in AC-Plasma Display Panels”, IDW '99, p. 72-75).
The above Japanese Unexamined Patent Application, First Publication No. 10-149767 proposes a PDP production method consisting of forming a protective film followed by temporarily forming a protective film having a low moisture permeability on this protective film, and then removing that temporary protective film. According to this method, during production of the PDP, since the surface of the protective film is protected by a temporary protective film, a deteriorated layer is not formed on the surface of the protective film. As a result, in addition to being able to obtain a protective film with satisfactory discharge characteristics, thermal decomposition treatment of a deteriorated layer on the protective film is not required.
In addition, in the above reference of W. T. Lee et al, together with suppressing deterioration of the MgO protective film by coating LaF3 having low moisture permeability onto an MgO protective film, it is proposed that higher secondary electron discharge characteristics and lower discharge characteristics can be realized.
However, in the production methods described in the above-mentioned Japanese Unexamined Patent Application, First Publication No. 10-149767 and the reference of W. T. Lee et al. of the prior art, it is difficult to conform the temporary protective film with the protective film when forming the temporary protective film, and there are cases in which cracks may form in the temporary protective film or the temporary protective film may peel off, thus making the effect of the temporary protective for preventing deterioration of the protective film inadequate. In order to improve this, although a method was considered in which a temporary protective film is laminated in a thick layer onto a protective film, in this method, there was the problem of a large amount of impurities (decomposition products of the temporary protective film) being formed during removal of the temporary protective film.
Moreover, in the above reference of W. T. Lee et al., 5-90 nm of LaF3 are laminated onto MgO and in this double layer structure, when the LaF3 of the upper layer film is removed by sputtering, there was the problem of an adequate lifetime being unable to be obtained due to sudden changes in the discharge voltage.
In addition, alkaline earth metal oxides are used as vapor deposition materials that serve as the raw materials for forming a superior protective film as described above.
However, similar to MgO films, if these alkaline earth metal oxides are exposed to the atmosphere before being used as vapor deposition materials, they re easily deteriorated as a result of reacting with CO2 and H2O. Consequently, it is own that, after placing vapor deposition materials comprised of alkaline earth metal oxides in a vacuum container, degassing exhaust treatment for a long period of time while heating in a vacuum is required. Namely, if degassing exhaust treatment is not performed for a comparative long period of time, impurity gases such as H2O, H2, O2, CO, CO2 and N2 generated in large amounts from the deteriorated surface of the vapor deposition material cause problems in the characteristics of the resulting protective film.
In addition, as an example of a manufacturing device for producing a protective film as described above, a manufacturing device for FPD protective films is disclosed comprising coupling a loading chamber that loads substrate onto a line, a heating chamber that heats the substrates, a film formation chamber in which a film body is formed on one surface of the substrates, a cooling chamber that cools the substrates, and an unloading chamber that unloads substrates from the line, without exposing them to the atmosphere (inline system), whereby a protective film is formed by electron beam vapor deposition and so forth at a predetermined region on the substrates (see, for example, Ulvac Technical Journal, No. 46, pp. 8-13 (1997), 7th Fine Process Technology Japan '97 Seminar preliminary collection of papers, D5, pp. 35-42 (1997)). In a manufacturing device for FPD protective film composed in this manner, since the process is carried out from loading to unloading of substrates without exposing the process to the atmosphere, improved productivity and conservation of space can be realized.
On the other hand, as examples of an apparatus for treating materials with a gaseous fluoridation agent, a dry etching apparatus that performs treatment with a mixed gas of HF and H2O for removing silicon oxide films on silicon wafers (see, for example, Japanese Patent Publication No. 2741546, Published Japanese Translation No. 6-26206 of PCT International Publication, Monthly Semiconductor World, [3], pp. 121-123 (1988), the Excalibur paper phase cleaning system described in the catalog of MFSI Co., Ltd., and the Falcon HF reduced pressure gas phase etching system described in the catalog of ASM Japan Co., Ltd.), and a surface treatment method and its apparatus for surface treatment of polyolefin resin molded products, polypropylene resin, carbon black and plastic molded products with a mixed gas containing fluorine, are disclosed (see Japanese Unexamined Patent Application, First Publication No. 10-101830, Japanese Unexamined Patent Application, First Publication No. 10-204195, Japanese Unexamined Patent Application, First Publication No. 9-40881 and Japanese Unexamined Patent Application, First Publication No. 10-182861).
In the above-mentioned dry etching apparatus for silicon wafers, dynamic systems, in which after performing treatment by introducing a gaseous fluoridation agent at a constant concentration into the system at nearly atmospheric pressure, inert gas is introduced followed by removal of residual gas, and closed systems, in which treatment is performed by introducing a gaseous fluoridation agent at a constant pressure into the reaction under a vacuum, returning the system to a vacuum, and after removing the residual gaseous fluoridation agent, inert gas is introduced and the system is returned to atmospheric pressure, have been proposed. These apparatuses allow selective etching of various types of silicon oxide films on silicon wafers by optimizing the mixing ratio of HF and H2O, HF concentration or HF partial pressure, reaction temperature, reaction time and so forth. Moreover, this dry etching apparatus enables particle generation to be reduced in comparison with wet etching. In addition, in the method and its apparatus for surface treatment of polyolefin molded products, polypropylene resin, carbon black and plastic molded products, etc. with a mixed gas containing fluorine, by making the surface of the treated material hydrophilic, dispersivity in aqueous solutions as well as coating, adhesion and other characteristics can be improved.
However, in the above manufacturing device for FPD protective film of the prior art, there is the risk of the protective film easily deteriorating as a result of reacting with CO2 and H2O if the protective film is exposed to the atmosphere after forming. In order to prevent this deterioration of the protective film, a method and apparatus have been considered that contact the protective film with a gaseous fluoridation agent to form a fluoride film on the surface of the protective film. However, in this fluorinating treatment method and apparatus, since FPD substrates are typically formed from glass, the substrate easily corrodes and becomes clouded, namely there was the problem of the FPD display surface and outgoing circuits around the FPD protective film ending up being clouded.
On the other hand, a treatment apparatus and method are disclosed composed such that substrates are placed nearly level in a chamber isolated from the surrounding environment, and regulatory gas containing a reactive gas is fed into the chamber to regulate the substrates (Published Japanese Translation No. 10-512100 of PCT International Publication). In this apparatus, a high-pressure gas inlet region into which regulatory gas is introduced is formed in the upper portion of the chamber, and a low-pressure regulation chamber that houses substrates in the center of the chamber is formed that regulates the substrates with the above regulatory gas. The above gas inlet region and regulation chamber are partitioned by a first pressure bias means comprised of a porous plate. In addition, a second pressure bias means is provided in the lower portion of the chamber that directs the flow of regulatory gas on the surface of the substrates to the outside and causes it to move in the direction of the outer periphery of the substrates, while an exhaust outlet is provided around or in the center of the lower end of the above substrates that discharges the above regulatory gas. This exhaust outlet is connected to an exhaust means.
In the treatment apparatus composed in this manner, high-pressure regulatory gas that has entered the chamber from the gas inlet portion is reduced to low pressure by the first pressure bias means and becomes a viscous flow. After chemically reacting with the substrate surface, it uniformly flows to the outside of the substrate surface and is discharged through an exhaust outlet around or in the center of the lower end. As a result, even in the above treatment apparatus, there was the problem that, although corrosion of the bottom surface of the substrate can be prevented, if regulatory gas makes contact with the portion at which the FPD protective film is not formed on the ends of the substrate surface in the same manner as described above, namely the outgoing circuits, and gaseous fluoridation agent is contained in the regulatory gas, the ends of the substrate surface end up being corroded.